Background: It is suggested that central augmented pressure (AP) and augmentation index (AIx) are due to wave reflection from peripheral to central arterial impedance mismatching. Comparatively stiffened peripheral vasculature should equate to increased AP and AIx. However, recent evidence suggests aortic reservoir characteristics may be a more dominant contributor to AP and AIx. This study aimed to determine relationship of central to peripheral impedance mismatch with, and predictors of, AP and AIx.

Methods: Carotid-to-femoral (aortic) pulse wave velocity (aPWV) and carotid-to-brachial PWV (bPWV) were measured in 255 patients with treated hypertension (aged 64±8, 47% male). Central AP, AIx and aortic reservoir pressure were derived from radial tonometry. Participants were stratified according to ‘high’ (bPWV > aPWV, n=64) or ‘low impedance mismatch’ (bPWV ≤ aPWV, n=191).

Results: Conflicting with theoretical expectations, central AP and AIx were significantly higher in participants with low-impedance mismatch compared to those with high-impedance (11±6 vs 7±6 mmHg, p=0.001 and 24±10 vs 21±13 %, p=0.05). Furthermore, impedance mismatch (bPWV-aPWV) was negatively and independently associated with AP (r=0.-0.13, p=0.04) and not associated with AIx (r=0.-0.001, p=0.99). However, aortic reservoir pressure was a positive independent predictor of AP and AIx (r=0.80 and r=0.62, p<0.001 for both).

Conclusions: Contrary to prevailing theory, ‘high-impedance’ mismatch between central and peripheral arteries does not result in higher AP or AIx. Aortic reservoir characteristics, rather than discrete wave reflection from impedance mismatching between peripheral and central arteries, may better explain AP and AIx.